As a cognitive phenomenon, mind-wandering provides researchers with a unique opportunity to study the control of thought through these momentary attentional deviations from the external environment. The broad objective of this proposal is to use the experimental and ecological study of subjective experience and task performance in order to better understand individual differences in the control of attention. At times when mind-wandering will interfere with the execution of a particular task, people may have different degrees of success at maintaining task focus. It is these individual differences in the ability to remain focused on one's task that may illuminate the underlying mechanisms of attention control during high-level cognition. Working memory capacity (WMC) is thought to reflect the ability to control attention (Engle &Kane, 2004) and therefore, we expect individual differences in WMC to reliably predict mind-wandering behavior. I will examine laboratory and daily-life situations in which the control of attention is necessary to perform well, but in which it is also highly variable, as demonstrated by off-task thoughts or mind-wandering. This research will combine experimental, correlational, and experience-sampling methods to explore the connection between individual differences in WMC and the nature of conscious experience and conscious control. WMC and mind-wandering behavior have a significant impact on the health and well-being of an individual. Individual differences in WMC have shown to be predictive of several mental health disorders, including ADHD and early onset Alzheimer's. Mind-wandering and other lapses of attention have potentially dangerous consequences in situations where the task requires sustained attention (e.g., driving a car). Moreover, by assessing the content of participants'mind-wandering experiences in these studies, I may also learn about the individual and contextual predictors of worry and rumination. Understanding the nature of mind-wandering and its predictive factors is important in the prevention of accidents and health-related consequences of attention lapses. A potential indicator of the ability to control attention and avoid accidents is working memory capacity and therefore this research seeks to understand the relationship between working memory capacity and mind-wandering using a unique combination of experimental, correlational, and experience sampling methods. Moreover, the proposed research will improve our understanding of working memory and executive function, which are central to a number of psychological and neurological disorders.